1. Technical Field
This invention relates to a medical apparatus suitable for accessing a target site within the body of a patient, and more particularly, to an introducer sheath suitable for use in introducing an interventional device into a bodily passageway of a patient.
2. Background Information
Introducer sheaths are in widespread use in the medical field for delivering a medical interventional device, such as a stent, to a target site within a bodily passageway of a patient, such as the vasculature. In order to reach the target site, the sheaths are often required to traverse tortuous pathways having sharp bends and angles. In some instances, and particularly when traversing such tortuous pathways, the sheaths exhibit a tendency to kink. Kinking reduces, and often collapses, the effective inner diameter of the sheath, thereby typically rendering the sheath unsuitable for its intended use.
The tendency of a sheath to kink is increased when the sheath is used to introduce the interventional device into one of the many smaller vessels that branch off from major vessels. In this event, the sheath may have insufficient flexibility at the very point where flexibility is most desired in order to enable proper positioning of the interventional device. In order to traverse the narrow confines of, e.g., the vascular system, the introducer sheath is typically formed of thin-wall construction. However, thin wall sheaths often have difficulty tracking narrow vessels, and exhibit an increased propensity to kink. Increasing the thickness of the sheath wall can minimally improve the level of kink resistance, as well as the trackability of the sheath. Any such increase in thickness, however, is inherently undesirable. The thickness increase limits the ability of the sheath to enter a narrow vessel, and reduces the diameter of the lumen when compared to the lumen of an otherwise similar thin-walled sheath. In addition, a larger diameter sheath necessitates the use of a larger entry opening than would otherwise be required or desirable.
One introducer sheath with improved kink resistance is disclosed in U.S. Pat. No. 5,380,304 to Parker. The introducer sheath described in the '304 patent comprises an inner liner formed of a lubricious fluoropolymer, such as polytetrafluoroethylene (PTFE). A coil is fitted around the inner PTFE liner, and an outer jacket formed of a heat-formable material, such as nylon or a polyether block amide, surrounds the inner liner and coil. The heat-formable material is heat shrunk onto the PTFE outer surface by enveloping it in a heat shrink tube, and heating the entire assembly until the material melts. As the heat-formable material melts, it flows between the spacings of the coil turns, and bonds to the outer diameter of the PTFE layer. The use of the coil in this device reinforces the sheath wall, and provides enhanced kink-resistance to an otherwise thin-walled introducer sheath.
The introducer sheath described in the '304 patent has proven to be particularly effective in delivering medical devices and medicaments to remote areas of a patient's vasculature without kinking. In order to minimize the cross-sectional profile (i.e., the outer diameter) of the sheath, the coil is generally formed of flat wire, as shown in FIG. 2 of the patent. By utilizing a flat wire coil, the sheath achieves a high level of kink resistance, and at the same time, maintains a low cross-sectional profile. The sheath described in the '304 patent enables the physician to routinely access, without kinking, target areas of the vasculature that had previously been difficult, or impossible, to reach.
With the continuous advances in the medical arts, more and more features have been developed to enhance the use of such introducer sheaths. For example, in order to improve the trackability of such sheaths, introducer sheaths have been developed wherein the proximal end of the sheath has a higher stiffness, while the distal end has a lower stiffness. One such sheath is disclosed in U.S. Patent Publication No. 2001/0034514. Since the distal portion of the sheath has a lower stiffness (and therefore is more flexible) than the proximal portion, the sheath is able to traverse portions of the anatomy that would have been difficult, if not impossible, to traverse with stiffer sheaths. Since the proximal portion has a higher stiffness (and is therefore less flexible) than the distal portion, the sheath maintains the trackability to traverse tortuous areas of the anatomy. This presence of the coil reinforcement also enables this sheath to be kink resistant through a wide range of bending angles.
U.S. Pat. No. 6,939,337 discloses a sheath having a coil reinforcement, as well as a braid reinforcement positioned over (i.e., radially outwardly of) the coil. This sheath utilizes a coil for the purposes of providing kink resistance in the same manner as the '304 patent and the patent publication recited above, and also includes a braid to enhance torqueability and pushability of the sheath. Each of the patent references cited above is incorporated herein by reference.
The improvements cited above have enabled the medical professional to more easily access areas of the vasculature that had previously been difficult, if not impossible, to reach. It is desired to continue to make advancements to enhance usage of such devices.